1. Field of the Invention
The invention relates to a spring-assisted lifting mechanism, such as a door or shutter, for a dishwasher.
2. Discussion of the Related Art
The spring-assisted lifting mechanism is used, in dishwashers for the catering trade, to facilitate the operation of raising a covering means covering the dishwashing chamber. The spring-assisted lifting mechanism is intended to bring about a smooth-running movement of the covering means between a bottom position and a top position, the covering means being retained in the bottom position by its own weight and the [sic] retained in the top position by a spring force.
A known spring-assisted lifting mechanism for a covering means of a catering-trade dishwasher comprises two levers mounted on a shaft, the covering means being mounted in a rotatable and displaceable manner on the first lever, and a tension spring acting at the end of the second lever. The shaft, on which the levers are mounted, is fixed on the frame of the dishwasher via the second lever, with the aid of the spring, a moment is applied to the shaft. This moment brings about or assists a rotation of the shaft and/or of the first lever, with the result that an opening movement of the covering means is facilitated. In order to ensure vertical movement of the covering means, the covering means is guided, on the rear side, in a guide fitted on the frame of the dishwasher.
However, this lifting mechanism has considerable disadvantages. For example, a high force is necessary for the purpose of opening the covering means since, in this position of the lifting mechanism, the spring only acts on the shaft with a small effective lever length. As the covering means is opened to an increasing extent, the effective lever length increases, with the result that the lifting force acting on the covering means becomes greater and greater. During this opening operation, the operator initially senses a high resistance because the opening movement is only assisted to a minimal extent. Since the operator applies the force in accordance with the necessary opening force, the covering means is often displaced upward against a stop at high speed. This takes place because, on account of the improving lever arm between the spring and the shaft, the force which is to be applied by the operator decreases as the degree of opening increases. It is also the case that during closure of the covering means the properties of the mechanism result in an undesired, disadvantageous force profile. This is manifested in that first of all a large force and then an increasingly smaller force has to be applied in order to move the covering means from the top position into the bottom position. This characteristic of the lifting mechanism results in the operator first of all having to apply a large force in order to set the covering means in motion and then, on account of the resistance becoming lower, has difficulties in slowing down the covering means before the bottom position has been reached.
The object of the invention is to develop a spring-assisted lifting mechanism which, in all positions of the covering means, provides a load-relieving moment, which is adapted to the requirements of the operator, and thus allows exact, high-precision operation of the covering means with a small manual force.
The spring-assisted lifting mechanism for the covering means according to the invention comprises a control means which is arranged between the second lever and the tension spring a which brings about a more or less constant effective lever between an articulation point of the spring and the shaft over an angle of rotation of the shaft of up to approximately 100 degrees. This achieves the situation where the opening movement of the covering means is assisted by a virtually constant force, with the result that a force profile which is not, expected by the operator is not produced either during raising or during lowering of the covering means.
According to a preferred embodiment of the invention the control means is configured as an intermediate lever which is connected to the second lever and the tension springs In this case said intermediate lever at times is retained freely between the articulation points and at other times butts rotatably and displaceably against a support. This design allows a cost-effective, straightforward and space-saving embodiment of the lifting mechanism with more or less constant spring assistance.
An advantageous embodiment of the subject matter of the invention makes provision for the control means to be configured as a triangular compensating lever or toggle lever. Such a configuration of the control means allows the shaft to be used as a support and thus the design to be particularly straightforward.
According to a variant of the subject matter of the invention, it is provided that [sic] to design control means as a bolt which is mounted in two guide means and on which the spring is fastened. The guide means are formed by a slot in the second lever and by a fixed guide. This likewise makes it possible to provide a constant torque on the shaft since the effective lever remains constant.
A further variant of the subject matter of the invention provides that the second lever has a cam-like head, over the end side of which there runs a cable or band, the spring being fastened at the free end of said cable or band. If the end side of the cam is designed such that it is located on a circle around the shaft, then it is also possible in this case, with the aid of the spring, to apply a constant moment to the shaft.